The invention relates to a sputtering installation with two longitudinally extending magnetrons, which are disposed next to one another and each have a target on an upper side thereof. Below the target, there is a U-shaped basic body, in which magnets, consisting of external and internal magnets, are enclosed. Between ground and one of the targets, there is a positive voltage, and between ground and another one of the targets, there is a negative voltage.
Sputtering installations with such longitudinally extending magnetrons lying next to one another, are known. In these installations, the target can be constructed in one piece or consist of several sections, preference being given to the latter variation.
During sputtering, material is ejected from the target and then deposited on the work, which is to be coated in the sputtering installation. During this sputtering process, material is not removed uniformly; instead, so-called erosion troughs are formed. The line linking the deepest places of this erosion trough is referred to as a directrix in that a partition of a weakly magnetic material is disposed between the two magnetrons and/or in that known shunts, that is insertions of weakly magnetic material, are introduced between the external and the internal magnets, the shunt on the side close to the respective other magnetron having a larger width than the shunt on the side averted from the respective other magnetron.
A target is to be regarded as consumed when the erosion trough, even at only one site of the target, is so deep, that the thickness of the material at this site is less than a threshold value. For this reason, efforts are made to ensure that the erosion trough is as wide as possible and to see to it that it has a uniform depth.
However, in the case of the sputtering installations mentioned, with two longitudinally extending magnetrons, it has turned out that the erosion trough at one end of the target is significantly deeper than in other regions. As a result of this deeper erosion, the targets are consumed significantly more rapidly.
Due to construction of such magnetrons with external and internal magnets, a longitudinally extending, but nevertheless ring-shaped magnetic field is developed.
The target voltages at the magnetron are poled differently. This means that, at a particular time, a positive voltage is applied between one target and ground and a negative voltage between the other target and ground. The target voltages and the ring-shaped magnetic fields bring about ring-shaped flows of electrons in the target. At a subsequent time, the polarity of the two voltages is changed. The directions of the electron flows within the target are determined by the polarities of the magnet arrangements.
It has now turned out that the sites at which there is a greater deepening of the erosion trough are at those ends of the magnetron at which the electron streams are directed to the respective other of the two magnetrons.
It is therefore an object of the invention to increase utilization of targets in sputtering installations wherein magnetrons lie next to one another.
Pursuant to the invention, this objective is accomplished due to the fact that a discharge resistance of a magnetron along a directrix is homogenized in such a manner that a partial discharge resistance of a target point on the directrix has the same magnitude as the partial discharge resistance of a different target point on the directrix in that a partition of a soft magnetic material is disposed between the two magnetrons and/or in that known shunts, that is insertions of soft magnetic material, are introduced between the external and the internal magnets, the shunt on the side close to the respective other magnetron having a larger width than the shunt on the side averted from the respective other magnetron.
The discharge resistance of the magnetron as a whole is determined by by a ratio of the target voltage to the target stream. As a result of the two-dimensional distribution of the target, the discharge resistance also experiences a distribution on the whole target, so that the discharge resistance actually arises out of the sum of a plurality of partial discharge resistances.
It is observed that, by homogenizing the discharge resistances along the directrix, deepening of the erosion trough at ends of the magnetrons, where the electron streams are directed to the other magnetron, are reduced appreciably.
In a particular development of the invention, provisions are made that a partition of a soft magnetic material is disposed between the two magnetrons. By means of such an arrangement of a partition, it is achieved that the magnetic fields of mutually adjacent magnetrons can affect one another appreciably less. With that, it is achieved that the magnetic field within a magnetron is almost the same on both sides. With such a regulation of the magnetic field, a homogenization of the discharge resistance is attained in a special manner.
In a further advantageous development of the invention, provisions are made that shunts, which are known and are inserts of a soft magnetic material, are introduced between external and internal magnets. The shunt on a side close to the other magnetron is wider than the shunt on side distal the other magnetron. With such an arrangement it has been observed that the magnetic field can be made to be almost the same on both sides of a magnetron. With that, a significant reduction in the mutual effect of the two magnetrons on one another is attained and a homogenization of the discharge resistance is also achieved.
It is particularly advantageous to provide a partition as well as shunts of different widths. Consequently, a particularly appropriate embodiment of the invention includes two adjacent magnetrons having soft magnetic shunts of different widths with wider width ones of the shunts being disposed on the side of the magnetrons adjacent the other magnetron and a partition member, formed of soft magnetic material, disposed between the two adjacent magnetrons.